Cathedral roof insulation: The insulation of choice for characterful buildings

19/05/2021

cathedral insulationFew buildings can compare in grandeur and magnificence to Cathedrals. The architecture of the intricate and intelligently composed design is timeless, priceless and something to be preserved. However, it is very difficult to fit insulation and achieve airtightness due to the complexity of the construction, owing mostly to the geometric design of the traditional high ornate ceiling. Therefore, when faced with the challenge of upgrading the insulation to keep the congregation warm in winter and cool in summer, there is a fine line to tread, balancing the level of insulation needed, whilst still maintaining the character of the building. The trick is to get the best of both worlds, but without the right material, this can be a thankless task. With 20 years of R&D in high performance, breathable multifoil insulation, TLX can help overcome the many problems associated with difficult to insulate buildings.

Providing a comfortable internal environment:

Air can sometimes leak from inhabited rooms into the roof space above. This can be brought on by a variety of factors including plumbing or electrical work penetrations into the ceiling. If not properly managed with insulation, this could potentially cause condensation, since air carries moisture, and when it reaches the cold side of the roof, it rapidly cools. Therefore, this risk needs to be managed by the careful placement of ventilation within the build-up.

The importance of ventilating in the right place:

Limiting the risk of condensation:
In a traditional roof system, ventilation would be introduced at the eaves, allowing any moisture carried into the roof space from below to escape; This goes a long way to limit the risk of condensation. With a warm roof construction, the trick is to minimize heat loss underneath the top layer of insulation as much as possible to gain the full benefit. For example, TLX Gold requires a minimum 10mm unventilated air gap underneath to keep the heat in. If the space within the rafters permits, a 20mm unventilated air gap is optimum for heat reflection.
TLX Gold intelligently limits the risk of condensation as it is fully breathable; therefore, it allows any water vapour entering the roof space to pass through it whilst reflecting heat back from its shiny underside.

TLX Insulation options:

Semi-exposed rafter solution:
If your cathedral roofline needs to be maintained as much as possible, this can be achieved with the use of TLX Gold. Laid over the top of the rafter space and counter-battened above with 38x38mm battens, TLX Gold will sag into the rafter space by approximately two thirds of its thickness, plus an optimum 20mm unventilated air gap underneath to allow for the heat to be reflected from its shiny undersurface. Plasterboard can then be cut to fit in-between the rafters, maintaining the character underneath, meaning anything lower than the top 40mm of the rafter will be exposed to the inside of the building. However, if your rafters are shallow, this build-up may not always be feasible. Therefore, you may need to consider completely exposing the rafter and raising the roofline by adding a plasterboard directly above the rafter and building your insulation profile up from there.

Fully exposed rafter solution:tlx gold historic buildings

TLX Gold is the perfect addition to ensure complete airtightness and a thermally efficient structure. It can be installed in one of two ways, either draped directly over the top of the rafter or pulled taut and counter battened. If the rafters are to be left fully exposed, whether it be to maintain the character or to save internal space, the roof may be boarded, then a 50mm counter batten is laid above the board with TLX Gold draped over the top of this. The counter-batten acts as a mini rafter. The shiny undersurface of TLX Gold is fully breathable, yet it reflects heat, therefore an optimum 20mm unventilated air gap should be maintained to facilitate heat retention within the building. As a single layer, TLX Gold achieves a U value of 0.69w/m2k. If a lower U value is required, then PIR board should be laid directly above the plasterboard to the desired thickness. The thicker the PIR board, the lower the resultant U value will be. However, it should be noted that adding additional insulation will raise the roofline.

U value requirements:

Historic buildings are sometimes listed and therefore building regulations are waivered in favor of preserving their character. Therefore, a simple improvement with the implementation of TLX Gold over the rafters will provide a significant thermal energy saving. However, building regulation Part L1B requirements currently stipulate a u value of 0.18w/m2k for non-listed buildings. The U value achievable will vary greatly according to the specific requirements and limitations of your project, such as rafter depth, rafter centers and the amount of additional insulation used. A completely uninsulated roof has a U value of 3.85w/m2k, Therefore, reducing this to 0.69w/m2k with TLX Gold alone is a great energy saving of 82%. If used as part of a hybrid system with the addition of PIR board of various depths, this will provide extra thermal benefit and U values as low as 0.13w/m2k can be achieved.


For bespoke U value calculations, please don’t hesitate to call our helpful team of product scientists on 01204 674 730.

We have written a number of case studies featuring histroic buildings, further details HERE.

All LABC registered TLX Gold solutions can be found HERE

tlx insulation technical department